The search for hidden radioactive material or the sensitive characterization of the radiation field created, for example, by a nuclear research facility is often performed by mobile, portable, and wearable instruments that contain very sensitive scintillation detectors. Such instruments are typically designed solely for the detection and spectroscopic analysis of gamma radiation using scintillator materials such as NaI(Tl), CsI(Tl), LaBr3(Ce), CeBr3, even though the detection of neutron radiation may also be desirable, in order to cover scenarios where dangerous and highly radiotoxic material, such as Plutonium or industrial neutron sources (e.g., AmBe or Cf-252) have been heavily gamma shielded or been masked by other radioactive material. However, instruments that are designed for both gamma and neutron radiation detection are significantly more expensive. Additional inconvenience and cost of ownership often arises by the need to calibrate the additional neutron detector. Examples for such detectors are gas filled proportional counter tubes with He-3, B-10 gas, or B-10 wall coating. Neutron sensitive scintillation detectors containing Li-6 are also known, such as LiI(Eu). Recently, gamma/neutron spectroscopic crystals such as Ce-doped Cs2LiYCl6 (“CLYC”) or Cs2LiLaBr6 (“CLLB”) have become available. These scintillation detectors are dedicated for spectroscopic gamma measurement and neutron detection, but instruments based on these crystals may become unable to detect neutron radiation in the presence of high intensity gamma fields.
Neutron activation analysis is a well-known technique to determine the concentration of trace elements in a sample. For conventional neutron activation analysis, the sample material is first exposed to a high neutron fluence rate, and then taken out of the neutron field and placed next to a spectroscopic gamma detector. The delayed gamma radiation of radio isotopes that were generated by neutron capture or other neutron induced nuclear reactions is measured and analyzed to determine the concentration of certain elements. Inverting the purpose of the measurement, neutron fluence measurements can be performed by irradiating a known metal foil in a neutron field of unknown strength. Disadvantages of this method include the need to actively perform these measuring steps, the limited detection sensitivity for low exposure scenarios, and the potential radiation exposure of the user handling the target material in high exposure scenarios.
A scintillator material containing Iodine has recently been used for measurement of pulsed neutron radiation. See PCT Application PCT/JP2014/056812 of Nohtomi et al, published as WO 2014136990 A1, hereby incorporated by reference in its entirety (however, where anything in the incorporated reference contradicts anything stated in the present application, the present application prevails). Here, 1-128 was generated by neutron capture and the emitted beta radiation was absorbed in the scintillator crystal and detected. The limitation and disadvantage of this technique can be seen in FIG. 1 in the wide and continuous distribution of beta energies ranging from 0 to approximately 2 MeV, due to the decay energy being shared between an ionizing particle (electron) and a non-ionizing particle (anti-neutrino). Thus, it is difficult to distinguish the induced radioactivity from the background radiation in, for example, low exposure scenarios. Furthermore, this method is limited to scintillation crystals containing Iodine, such as NaI(Tl) or CsI(Tl).
Therefore, there is a need for further improvements in detection of neutron radiation by neutron activation of scintillator materials.